Geodetics measurements within the scope of current and future perspectives of GNSS-Reflectometry and GNSS-Radio Occultation Introduction The aim of this presentation is to provide an overview of the GNSS-R and GNSS- RO concept both in theory and application. Investigation of direct, reflected and bent MW GPS signals and its capability for sensing the Earth s environmental transition impacted by the global warming. FIG Working Week 2015 1
GNSS signal ability: GNSS-Reflectometry: Sensing land and soil moisture, the ocean and sea roughness including monitoring wind speed and wind-driven waves. Monitoring of the polar ice sheets, snow thicknesses, glaciers, their surrounding sea s level and estimating new ice on the Arctic region. GNSS-Radio Occultation: Weather and climate forecasting; atmospheric sounding which include water vapor, temperature and pressure GNSS-Reflectometry GNSS-Reflectometry measures reflected navigation satellite signal from water, ice or wet land surfaces GPS satellites are constantly broadcasting radio signals to the Earth and some of these signals are reflected back from the rough Earth's surface FIG Working Week 2015 2
GPS Transmitter GPS Receivers (RHCP and LHCP) Specular point Glistening zone GNSS-R, elements of reflections Reflected signal is scattered in different directions A majority of the signals reaching the receiver reflects of an area called the glistening zone Size of glistening zone depends on the surface roughness, incidence angle and receiver height Specular point is physical contact of signal with surface in glistening zone FIG Working Week 2015 3
GNSS-Reflectometry The receivers were carried either by space platforms (LEO orbit) or by aircraft and stratospheric balloons or based on the ground Space-based Instruments 1/2 LEO Orbit (piggy pack) Day and night operation without the influence of the different weather conditions GPS L-band signals are sensitive to the atmospheric gas and plasma distribution over the ocean Possible to quickly detect a tsunami in the deep ocean. The early warning system of tsunami detecting, presents the large synoptic view of ocean in only 150 seconds for an area of 1000km x 1000km FIG Working Week 2015 4
Air-based Instruments 1/2 Working on the same principle as space-based, air-based instruments in general record the raw data on board the one aircraft (or balloon) and later postprocessed them in a laboratory. Main parameters to observe over the sea surfaces are: Wind speed at 10 m Duration of the wind The fetch (the distance over which sea surfaces wind was blowing at the constant speed Air-based Instruments 2/2 Challenges: The airplane position is not stable, causing a change in the distance between the transmitter and the receiver ( characterized by a Doppler effect) The characteristics of the sea surfaces is divided into three stages : 1. Creation of a theoretical model (Input Elfouhaily Model into Kirchhoff Model helps to estimate and understand the expected behavior of scattering signal from glistening zone) 2. Creating the Delay-Doppler map (DDM) 3. Analysis of DDM ( characterization of the sea surfaces) FIG Working Week 2015 5
Air-based Instruments 2/2 Reflection power over the glistening zone for 1m/s and 10m/s Delay and Doppler plots for both speeds similar Ground based Instruments For local observation, many coastal and bridge experimental campaigns were done The accuracy of given results are more than satisfactory The main principle to accumulate and process measurement data for a long period continuously and compare with measurement in situ (e.g. Disko Bay - objective was to explore the sustainability of using reflected GPS signals to scrutinize properties of dry snow, sea-ice and the prediction of the ice age from space. Performance of GNSS is limited in the Arctic area compared to latitude (maximum elevation through a GPS reflection of 65 FIG Working Week 2015 6
GNSS-RadioOccultation Advantage : to augment current weather data sets to produce accurate weather results which consist of density profiles and temperature in different atmospheric layers like troposphere and stratosphere. Also measure is the ionospheric total electron content (TEC) which is involve in calculation of carrier phase delays of transmitted radio signals from satellites. GNSS-RadioOccultation The continuous radio signals are broadcasted until the GNSS signals set below the Earth s atmosphere (go down below the surface). GNSS signal bends due to the atmosphere of the Earth before it arrives to the receiver The signals that have passed through the Earth s atmosphere scan layers of the atmosphere and simultaneously determine the vertical profiles of the refractive atmospheric index FIG Working Week 2015 7
Conclusion Implementation of GNSS-Reflected measurements in monitoring of the current situation and future disasters prediction such as prediction of tsunami, monitoring ocean eddies, flooding and other observations of the Earth. Radio Occultation measurements have been proven also as good and accurate results compare to the results given by number of meteorological centers around the world. Relatively low cost of mission Future work In the near future, GNSS-R and GNSS-RO are expected to flourish as an emerging application in the field of remote sensing obtaining fast and accurate results. Future research will be focused on the capabilities of those techniques in terrestrial measurements and its benefits on possible replacement of present geodetic techniques of remote sensing. GNSS-RO has to be investigated in research for monitoring the Ozone Hole FIG Working Week 2015 8
Thank you! Danijela IGNJATOVIC STUPAR, France Karishma INAMDAR, India Andrew LEE CHEE HAU, Malaysia International Space University, France FIG Working Week 2015 9